diff -r dd55d54b2a15 Lib/test/test_struct.py
--- a/Lib/test/test_struct.py	Sun Sep 29 18:57:42 2013 -0700
+++ b/Lib/test/test_struct.py	Tue Oct 01 11:24:15 2013 +0300
@@ -574,6 +574,14 @@
         self.check_sizeof('0s', 1)
         self.check_sizeof('0c', 0)
 
+    def test_unicode_format(self):
+        # Issue #19099
+        s = struct.Struct(u'I')
+        self.assertEqual(s.format, 'I')
+        self.assertIs(type(s.format), str)
+        self.assertRaises(ValueError, struct.Struct, u'\x80')
+
+
 def test_main():
     support.run_unittest(StructTest)
 
diff -r dd55d54b2a15 Misc/NEWS
--- a/Misc/NEWS	Sun Sep 29 18:57:42 2013 -0700
+++ b/Misc/NEWS	Tue Oct 01 11:24:15 2013 +0300
@@ -32,6 +32,8 @@
 Library
 -------
 
+- Issue #19099: The struct module now supports Unicode format strings.
+
 - Properly initialize all fields of a SSL object after allocation.
 
 - Issue #4366: Fix building extensions on all platforms when --enable-shared
diff -r dd55d54b2a15 Modules/_struct.c
--- a/Modules/_struct.c	Sun Sep 29 18:57:42 2013 -0700
+++ b/Modules/_struct.c	Tue Oct 01 11:24:15 2013 +0300
@@ -1371,13 +1371,28 @@
 
     assert(PyStruct_Check(self));
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "S:Struct", kwlist,
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O:Struct", kwlist,
                                      &o_format))
         return -1;
 
-    Py_INCREF(o_format);
-    Py_CLEAR(soself->s_format);
-    soself->s_format = o_format;
+    if (PyString_Check(o_format)) {
+        Py_INCREF(o_format);
+        Py_CLEAR(soself->s_format);
+        soself->s_format = o_format;
+    }
+    else if (PyUnicode_Check(o_format)) {
+        PyObject *str = PyUnicode_AsEncodedString(o_format, "ascii", NULL);
+        if (str == NULL)
+            return -1;
+        Py_CLEAR(soself->s_format);
+        soself->s_format = str;
+    }
+    else {
+        PyErr_Format(PyExc_TypeError,
+                     "Struct() argument 1 must be string, not %s",
+                     Py_TYPE(o_format)->tp_name);
+        return -1;
+    }
 
     ret = prepare_s(soself);
     return ret;